A telescopic gunsight, hereafter referred to as a scope, is essentially a telescope containing an aiming reference point (reticle), for mounting on a rifle. The magnification provided by a scope generally offers many advantages over the iron sights found on most rifles. For example, a scope can increase the visibility of a distant animal or target and/or assist in the identification and location of game. Often, an animal that would ordinarily go unnoticed in protective cover stands out more clearly when viewed through a scope. Similarly, while deer hunting, a distant deer may appear as a buck or a doe through iron sights; with a scope, a hunter can more easily identify the sex of the deer and even determine the size of the buck's rack. A scope may also add a margin of safety to hunting by reducing the number of accidental shootings. What may look like a deer, bear or other animal with the naked eye may well turn out to be a camouflaged hunter when viewed through a scope. A scope may also serve as an aid to failing eyesight. For example, older hunters or shooters with reduced eye accommodation generally have difficulty with iron sights when trying to simultaneously focus the rear sight, the front sight and the target, which are all located at different distances from the eye. With a scope, this difficulty disappears because the image of a target or game is placed directly on the reticle. Consequently, when the shooter's eye is focused on the reticle, it is also focused on the target.
The primary function of a scope is to make a distant object look closer by making it appear larger. This function is achieved by the relative arrangement of the various lenses within the housing of the scope. Typically, rifle scopes are available in a wide variety of fixed powers ranging from approximately 1.5x to 30x or greater and with variable powers offering a broad range of magnifications including 11/2x to 6x, 3x to 9x, 6x to 24x and others. Although fixed power scopes are generally smaller, lighter and less expensive than variable power scopes, they are not as versatile and are limited in their application. In particular, the field of view (the width of the area visible through the scope) provided by a fixed power scope may not be appropriate for different types of hunting or shooting. For example, while the narrow field of view and greater magnification provided by a high power scope may be sufficient and desirable for target shooting or for long range hunting of stationary game, it is generally unsuitable for quick shots at a moving target or animal. Conversely, while the wider field of view provided by a lower power scope is highly important for close shooting or for running shots because it allows a target to be more easily tracked through the scope, the magnification provided by the lower power scope may not be appropriate for long range hunting or for competitive target shooting. Thus, a shooter must make a tradeoff between magnification and field of view when purchasing a fixed power scope.
A variable power scope avoids the above-described disadvantages of fixed power scopes by providing an adjustable range of magnification and an adjustable field of view. A variable power scope typically includes an elongated housing (main tube) containing a collective lens, an erector lens and an adjustable reticle, an ocular lens arrangement (eyepiece) located at the end of the housing nearest the shooter's eye, an objective lens arrangement located at the end of the housing closest to the muzzle of the rifle and a rotatably adjustable zoom lens arrangement located proximate the eyepiece or integral therewith. The magnification of a variable power scope may be quickly adjusted by manually rotating an element such as a ring or sleeve located about the perimeter of the zoom lens arrangement.
Correct hand positioning is essential for the proper support and immobilization of a rifle while aiming and/or shooting at a target. This is particularly true for rifles with scopes mounted thereon because the magnification provided by the scope increases the apparent tremors of the sight picture. For example, when holding a scope mounted rifle in the right handed shooting position, a shooter typically supports and stabilizes the forearm of the rifle with the left hand, tucks the butt of the rifle into the pocket of the right shoulder, grasps the pistol grip of the rifle with the right hand and positions the right eye according to the eye relief of the scope. In this position, the stock and forearm of the rifle are primarily supported by the fingers and palms of the right and left hands, respectively. In general, the index finger of the right hand is placed on or near the trigger of the rifle the middle, ring and pinkie fingers are secured around the underside of the pistol grip and the thumb is wrapped thereover. Similarly, the fingers of the left hand are commonly wrapped around the forearm of the rifle with the palm facing upwards. Unfortunately, in order to adjust the magnification of currently available variable power rifle scopes, a shooter must remove the rifle and/or one or both hands from the shooting position prior to any manual manipulation of the rotating element on the zoom lens arrangement, thereby resulting in the potential loss of a previously sighted target or animal from within the field of view of the scope and the possible forfeiture of a shooting opportunity.
A powered zoom rifle scope which utilizes a thumb operated switch located on the upper surface of the eyepiece to control a motorized zoom lens assembly has recently been developed in an attempt to overcome the above-described problem. Although it is an object of this scope to allow for the thumb actuated adjustment of the zoom lens assembly while maintaining a shooting finger on the trigger of the rifle, the location of the thumb manipulated switch requires the shooter to remove the thumb and palm of the trigger hand from their shooting position on the pistol grip of the rifle and to maneuver the trigger hand into a very unnatural and uncomfortable position. Consequently, the rifle may be prone to significant movement during the magnification adjustment of the zoom lens assembly, thereby resulting in the potential loss of a target from within the field of view of the scope. More importantly, however, the rotational movement of the trigger hand that is required to correctly position the thumb on the eyepiece switch tends to force the trigger finger of the shooter against the trigger of the rifle, possibly resulting in an accidental firing of the rifle.